Sutherland says laboratory tests show the DS4G it is four times more fuel efficient than the best ion engines available and 10 times more fuel efficient than used to propel ESA's SMART-1 Moon mission.

"The underlying technology has been around for 40 years," he says. "All we did with the DS4G is to add some extra components which basically gave it a 10-fold improvement."

Sutherland says missions to Pluto and the Kuiper Belt would be "quite easily" made, with trips out beyond the solar system also more feasible.

"All of that within the working lifetime of a mission scientist," he says.

Another option is the new engine could help take heavier missions to shorter distances such as the Moon or Mars.

How it works

A standard ion engine works by using electrodes to extract ions from plasma, in this case heated xenon gas.

The ions are focused into beams that accelerate through tiny holes in the electrodes and thrust metres out into space, propelling the spacecraft in the opposite direction.

The standard engine has only three electrodes, capable of generating up to 5000 volts between them.

Anything greater than this would cause the ion beams to miss the holes in the electrodes and hit the metal, destroying the electrodes and causing less efficient thrusting.

Sutherland found a way to add another electrode to the system and boost voltage up to 30,000 volts without the ion beams hitting the electrodes. He says, given enough power, it would be possible to generate 70,000 volts over the electrodes.

He says the bigger the voltage, the faster the ions in the beam accelerate, and the more efficient the propulsion.

ESA reports tests on DS4G produced an ion exhaust plume that travelled at 210,000 metres per second.

Trend towards ion propulsion

Sutherland says that over the past 10 years such ion propulsion thrusters have become more popular because they provide constant propulsion for a spacecraft.

By contrast, he says, conventional chemical thrusters, which rely on ballistics to get the spacecraft on the right path, give the spacecraft "one big kick" and then rely on it to coast along in space until it slows down.

Ion propulsion also means mission scientists can bettr control a spacecraft's steering, says Sutherland, compared to the one-off chemical thruster.

Nuclear powered?

Sutherland says the ion engine needs megawatts of power to generate the necessary voltage across the electrodes and to generate the ion-providing plasma.

"This particular thruster has high performance but the cost of that high performance is it requires more power to run," he says.

He says standard photovoltaic cells, as used on the SMART-1 mission, would not be adequate and an on-board power system would be required.

This would be necessary anyway if the engine was to propel a spacecraft into deep space where there is little available light, he says.

"People are talking about CTRs - controlled thermonuclear reactors - small plutonium chunks like, for example, the power system that just went up on the NASA mission to Pluto."

The DS4G, which was funded by ESA's Advanced Concepts Team, will undergo more testing before industry partners are sought for a mission, says Sutherland, who estimates this process will take at least 10 years.